1. Field of the Invention
The invention relates to the field of power transmission chains. More particularly, the invention pertains to a power transmission chain containing spacing elements to increase fatigue strength and decrease incidence of chain strand resonance.
2. Description of Related Art
One aspect of the invention relates to a silent or rocker joint chain, which has links having inverted teeth for engagement with an associated sprocket. Generally, rocker joint chains are used with sprockets for power transmission in transmissions, transfer cases, engine timing systems, and the like. Rocker joint chains are well known in the art. Examples include U.S. Pat. Nos. 5,651,746; 5,345,753; and 5,372,554 which are incorporated herein by reference.
Rocker joint chains are formed by the assembly of rows of links in lateral and longitudinal directions. Each link typically has a pair of teeth and a pair of pin apertures. The links are interlaced and then connected to each other by connecting pins inserted in each pin aperture. Guide links are utilized as the outermost links of the chain to maintain the chain on the sprockets when the chain is wrapped around the sprockets during operation. Guide links may be installed in the center or at both outer edges of the row of link plates arranged in the lateral direction. The guide links are conventionally press fit over pins, which connect the interlaced inside or articulating links. Guide links typically do not include inverted teeth.
Conventionally, a rocker joint is used as the connecting pin. The rocker joint is comprised of a pair of long and short pins. A first short pin, referred to as the rocker, is paired with a second longer pin. The longer pin has both ends fixed to guide links at the outmost flanks of the chain.
Conventional rocker joint chains are limited in the transfer of load between the rocker and the inside links that are positioned at the outermost end of the rocker. The limitation is due to the fact that only partial contact is obtained between these same inside links and the end of the rocker. A separate limitation concerns the contact between the outermost inside links and the sprocket. Due to the required chamfer on sprocket teeth and the axial clearance between the sprocket teeth and chain guide links only partial contact is achieved between the same inside links and the sprocket.
Prior art rocker joint chains showing the disadvantages in conventional chain designs are shown in FIGS. 1–3 and 14. The chain is comprised of rows of links. Alternate rows of links, or guide rows, have guide links press fit on their ends. The remaining rows, or non-guide rows, have inside links as their outermost links.
FIG. 1 shows a prior art rocker joint chain in a side view. Rows of inner links 21 in a guide row 12 alternately interleave with rows of inner links 21 in a non-guide row 14 and held by rocker joints comprising pairs of pins 16 and rockers 18. A guide link 20 is fixed to the each end of the guide row 12 of inner links 21 by pins 16 which extend outwardly from the rows of inside links.
In the prior art rocker joint chain 10, shown in FIG. 2, there is a clearance 30 between the end of the rocker 18 and the guide link 20. This clearance 30 exists because of necessary manufacturing tolerances of the individual rockers 18 so that they are spaced from the guide links 20 after the assembly process. There also exists an end radius 19 on the rocker 18, which is necessary to prevent excessive local stresses in the pin 16 and rocker 18, and also for ease of assembly of the chain 10. The clearance between the rocker 18 and the guide link 20 and the shortening of the rocker as a result of the end radius of the rocker, result in only partial bearing contact between the outermost inside links 22, 23 of the non-guide row, and the rocker. The partial bearing contact limits the load carrying capability of the chain because all of the links are not carrying their full share of the load.
FIG. 3 shows an exaggerated cross section through the chain of the prior art and sprocket 40. The chain 10 is shown slightly out of position, i.e., raised vertically. The limitation in this design is that the contact area between the outermost inside links 22, 23 and sprocket tooth 25 is limited due to the chamfer 26 on the sprocket teeth and the necessary axial clearance between the chain 10 and sprocket 40. Thus, the partial engagement or partial contact occurs between the outermost inside links 22, 23 of the non-guide row and the sprocket.
FIG. 14 shows a conventional rocker joint chain with a centered spring link 32. Spring links are used in chains conventionally, to help control chain strand vibration by increasing the internal friction in the chain. Compression of the centered spring link 32, in the direction shown by the arrow, forces the links in the rows to press against each other causing friction. The compression of the inside links 21 in the non-guide row 14 against the outside guide links 20 could cause a gap great enough that the rocker pin 18 may become disengaged from the outside guide links 20, forcing the non-guide row 14 of inside links 21 apart, resulting in a loss of chain strength.
The present invention also has application to silent chains with round connecting pins. An example of a round pin silent chain is shown in U.S. Pat. No. 4,758,209, which is incorporated herein by reference. While there is no rocker in a round pin chain, the spacing elements, especially when they are spring links, help center the inside links between the guide links. This helps provide full engagement of the inside links with the sprocket teeth, helping to distribute the load between the chain and the sprocket more evenly than in a chain without spacing elements. This affect is also beneficial in a rocker joint chain.
The present invention also has application to chain belts, as shown in U.S. Pat. Nos. 4,580,999 and 5,439,423 which are incorporated herein by reference.